Stirling engine control system

ABSTRACT

A working gas control system for a double acting hot gas engine particularly adapted for vehicle installation and including a manually adjustable system for variably controlling the pressure of the engine working gas to provide for load control of the engine. The system includes a gas reservoir for working gas to supply the engine system with gas at a suitable mean working pressure through an operator actuator control system. A gas supply tank is provided to maintain a predetermined minimum gas pressure in the reservoir.

United States Patent Bennethum Oct. 24, 1972 [54] STIRLING ENGINE CONTROL SYSTEM [72] Inventor: James E. Bennethum, Rochester,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: May 27, 1971 [21] Appl. No.: 147,355

[52] US. Cl ..60/24 [51] Int. Cl ..F03g 7/06 [58] Field of Search ..60/24 [56] References Cited UNITED STATES PATENTS 2,616,243 11/1952 Van Weenen ..60/24 2,794,315 6/1957 Meijer ..60/24 Reinhoudt ..60/ 24 Brandes ..60/24 X Primary Examiner-Martin P. Schwadron Assistant Examiner-A. M. Ostrager Attorney-Jean L. Carpenter and Arthur N. Krein [5 7] ABSTRACT 3 Claims, 5 Drawing Figures INVENTOR.

\Zmes 5. BennezE/zum ATTORNEY STIRLING ENGINE CONTROL SYSTEM This invention relates to hot gas engines and more particularly to a gas control system for a closed cycle hot gas engine such as a double acting Stirling cycle engme.

It is known in the art to provide means for controlling hot gas engines of the Stirling cycle type by varying the pressure of the working gas in the engine working spaces. Such pressure variations have been accomplished by supplying gas from external storage means to the engine working space and exhausting gas from the working spaces to the storage means through the operation of suitable transfer and control means including a gas compressor. Nonnal practice has been to use one small high pressure external gas reservoir to store the working gas and to serve as the source of gas to fill the engine during operation. However, it has been found that the use of such small high pressure reservoirs for the gas is disadvantageous because the. high pressure of the gas maintained in the reservoir requires relatively high compressor input power to refill the reservoir with gas discharged from the hot gas engine and the use of a high pressure reservoir did not allow. the system to make use of the hot gas engines own pumping ability to directly refill the gas reservoir from the working spaces of the hot gas engine under certain engine operating conditions.

It is therefore the principal object of this invention to improve hot gas engine control systems whereby the. power required for refilling the reservoir with gas exhausted from the engine is reduced.

Another object of this invention is to improve a hot gas engine control system whereby engine response times are small and independent of the engine duty cycle.

These and other objects of the invention are attained by means of an engine control system in which working gas is supplied to the engine by normal gas pressure flow from a supply reservoir through an engine pressure control system; a gas supply tank being provided to supply makeup gas to maintain a minimum gas pressure in the reservoir and to serve as a secondary reser voir to which gas can be bled if the pressure in the main reservoir exceeds a predetermined pressure at engine shutdown. Engine power is varied in a known manner by varying the gas pressure in the engine working space with pressure responsive regulating means being utilized to maintain the desired working space pressure by sensing the mean pressure in the working space and controlling the gas supply and exhaust in accordance with desired pressure requirements. The regulating means includes manually adjustable pressure selection means which are actuated by the vehicle operator such as through a conventional foot pedal to manually select the desired working gas pressure. The variation of this manual selection means thus varies the engine output torque and provides engine operation similar to that of the throttle controlled internal combustion engine.

For a better understanding of the invention, as well,

as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a cross sectional view of a double acting, four-cylinder, in line, hot gas engine of the Stirling cycle type;

FIG. 2 is a schematic illustration of the gas supply and pressure control system for the engine of FIG. 1;

FIG. 3 is a diagrammatic representation of the fluid pumping means in the system of FIG. 2;

FIG. 4 is a schematic illustration of the inlet and exhaust system to the engine of FIG. 1; and,

FIG. 5 is a sectional view showing the pressure control system of the gas supply and pressure control system of FIG. 2.

Referring now to the drawings, a four-cylinder, double acting, in line, hot gas engine, generally designated by reference numeral 10, includes cylinders 11 mounted on and partially closed at one end by an intermediate block 12 which in turn is supported on an engine crankcase 13. The cylinders 11 terminate in closed ends 14 at one end thereof and are partially closed at the opposite end by the apertured reduced portion 15 of the intermediate block 12.v Intermediate block 12 with annular apertured end caps 16 secured thereto support part of a rolling seal structure 17 for each piston. Each rolling seal structure may be of the type disclosed in U.S. Pat. No. 3,568,436 issued Mar. 9, 1971 in the names of Francis E. Heffner and Richard R. Toepel.

A non-vented piston 18 is slidably received in each of the cylinders 11 and is suitably connected at one end to the piston rod portion 19 of a crosshead piston 21 slidably received in a crosshead cylinder portion 22 of the crankcase 13, which may also bev provided with crosshead piston liners 23. Each crosshead piston 21, in turn, is connected by a connecting rod 24 to a crankshaft 25 joumaled in the crankcase 13, the connecting rods 24 being connected at their upper ends to the crosshead pistons 21 by pins 26 retained in the crosshead pistons by retaining rings 27.

The interiors of the cylinders 11 are separated by their respective pistons 18 i into hot chambers 28 formed at the ends 14 of the cylinders, and cold chambers, not numbered, formed at the opposite ends thereof. Canister-like members 30 encircle. each of the cylinders and support therein suitable coolers 31 and regenerators 32. A heater, not shown, which may be a burner or other suitable heating. device, is located above the canisters 30. A plurality of tubes 33 extend from the ends 14 of the cylinders through the heaters to the regenerators 32 of each cylinder. Connecting tubes 34 connect the coolers 31 of one cylinder'with the cold chamber end of the next appropriately phased cylinder.

Thus, four separate gas containing working spaces are formed, each made up of the hot and cold chambers of adjacent cylinders connected-through heater tubes 33, regenerators 32, coolers 31 and connecting tubes 34 in a known manner as shown in U.S. Pat. No. 3,538,706 issued Nov. 10, 1970 to Richard R. Toepel.

Referring to FIG. 2, there is shown schematically a control system diagram for supplying the working gas to the engine 10. A supply of working gas is contained in a supply tank 40 and a reservoir 41, the supply tank 40, which serves as a secondary reservoir being connected to the reservoir 41, by a supply conduit 42-with a pressure regulator 43 therein and by a return conduit 44 with a pressure relief valve 45 therein. The reservoir 41 is connected to a manifold type fill header 46 for supplying working gas to the engine by means of a conduit 47 through an engine pressure control regulator,

tion and it can be controlled by a conventional switch, not shown.

The fill header 46 is connected by valve controlled conduits 51 to the engine and gases are dumped from the engine through valve controlled conduits 52 to a manifold type dump header 53 which in turn is connected by conduit 54 to the engine pressure control regulator 48 and then by conduit 55 through a plurality of compressor gas chambers or accumulators 56 and 56a, and conduit 58 to the reservoir 41. Compressor gas chambers 56 and 56a are actuated by a compressor pump 57, as described hereinafter.

Referring now to FIG. 3, there is shown diagrammatica'tly the fluid pumping system for the engine which includes the compressor gas chambers 56 and 56a and the compressor pump 57. As shown, the device includes a pair of compressor gas chambers 56 and 56a in the form of accumulators, both of which incorporate movable wall means such as diaphragms 61 which divide these accumulators into first and second chambers 62 and 63, respectively.

Chambers 62 are connected through spring biased check valves 64 and conduit 58 to the reservoir 41. The valve openings for the check valves 64 include metal anti-extrusion flaps 65 which prevent damage to the diaphragms while permitting flow to the check valves 64. The chambers 62 are also connected through spring biased poppet inlet valves 66 and conduit 55 with the engine pressure control regulator 48 and therethrough with the working space of the engine 10. The valves 64 and 66 are arranged to permit flow from the engine working space to either chamber 62 and from either chamber 62 to the reservoir 41, but to prevent flow in the opposite direction as well as to prevent flow between the two chambers 62.

Chambers 63 of the compressor gas chambers 56 and 560 are connected through spring biased anti-extrusion devices 67 and conduits 68 and 68a, respectively, to spaced portions of the housing 70 of a spool type selector valve. Valve housing 70 also includes drain lines 71 and 71a located adjacent its ends and a hydraulic supply line 72 which connects with the output of the compressor pump 57 in the form of an oil pump, the drain lines 71 and 7 la being connected to the inlet of pump 57. The compressor pump 57 receives pressurized oil drained from lines 71 and 71a and oil bypassed through supply line 72 in a manner described in detail hereinafter.

Reciprocally disposed within valve housing 70 is a valve spool 73 which includes oppositely disposed end portions in the form of actuator rods 74 and 74a.

Each of the actuator rods 74 and 74a are selectively reciprocated by means of pivotally connected levers 75 and 75a, respectively, which in turn are pivoted clockwise and counterclockwise, respectively, by means of hydraulic actuated plungers 76 and 76a of pressure actuators 78 hydraulically connected to conduits 68 and 68a, respectively.

When the valve spool 73 is in the position shown in FIG. 3, the valve acts to connect hydraulic supply line 72 with conduit 68a, while conduit 68 is connected with drain line 71. In its second position, in which the spool valve 73 is moved to the right with reference to FIG. 3, it connects hydraulic supply line 72 with conduit 68 while conduit 68a is then connected with the drain line 71a.

The hydraulic system also includes a pressure release valve 81 connected with the outlet of the compressor pump 57 and is arranged to bypass fluid therefrom to the compressor pump inlet at a predetermined pressure. A bypass valve 82 is also connected to both the inlet and outlet of the compressor pump 57 and includes a valve spool 83 which is spring biased in an opening direction wherein the pump inlet and outlet are connected. A diaphragm actuator 84, at one end of spool 83, is acted on by gas pressure in conduit 55 through connection therewith by a line 85 for a purpose to be subsequently described.

The operation of the above-described compressor system is as follows. Compressor pump 57 in the form of an oil pump is driven intermittently, by an electric drive motor, not shown, the operation of which is controlled by a switch SW-l actuated by valve spool 83 of bypass valve 82. When, however, the compressor pump is in operation and the valve spool 73 is in the position shown in FIG. 3, oil is pumped through line 72 and conduit 68a to chamber 63 of the accumulator 56a. This forces diaphragm 61 upwardly reducing the size of chamber 62 therein and forcing any gas in this chamber out of accumulator 56a and past check valve 64 through conduit 55 to the reservoir 41.

When the gas in chamber 62 is exhausted and diaphragm 61 bears against the sides of the accumulator 56a, the hydraulic pressure in line 68a increases to force the plunger 76a of pressure actuator 78 associated with this line to the left, as shown in FIG. 3, to rotate the lever a counterclockwise to move the spool valve 73 to the right, as shown in this figure, thus connecting line 68a with drain line 71a. At the same time, line 72 is connected with conduit 68 so that the compressor pump 57 begins to fill chamber 63 of accumulator 56 forcing out of it any gas which may be present in its chamber 62 in the same manner as was done with accumulator 56a. When all gas is eirhausted from accumulator 56, the pressure in line 68 will increase, actuating the plunger 76 of pressure actuator 78 connected to this line to rotate the lever 75 associated therewith in a clockwise direction to move the spool valve 73 to the left, to the position as shown in FIG. 3, after which the above-described cycle is again repeated.

While the above-described pumping action is taking place in one accumulator, the full volume of the remaining accumulator is always available to receive a charge of gas from the engine 10 through the dump header 53, conduit 54, engine control system 48 and conduit 55.

Thus, when accumulator 56a is being discharged and the engine is cycled for full load to idle, the complete charge of gas is receivable through conduit 55 and check valve 66 into chamber 62 of accumulator 56. Since the gas is received under pressure, it easily forces out of chamber 63 the oil contained therein, which passes through conduit 68 and drain line 71 to the inlet of pump 57.

When the pumping cycle on accumulator 56a is then completed, the valve spool 73 is moved as previously described and the discharge of gas from accumulator 56 is begun. At this time, accumulator 56a is available to receive an additional charge of gas from the engine working space through conduit 55 and check valve 66 to chamber 62 of the accumulator 56a.

Whenever the gas pressure in line 55 drops to a predetermined low pressure, such that further pumping action of the compressor is not required, the reduced pressure on diaphragm actuator 84 permits the valve spool 83 to move to the left, as seen in FIG. 3, opening the bypass valve 83 and bypassing hydraulic fluid discharged from the pump 57 back to the pump inlet.

This stops further gas pumping action until increased inlet pressure in line 55 again closes the bypass valve 82. In addition, when the spool valve 83 moves to the left, as described above, the contacts of switch SW-l are opened thus deenergizing the electric motor used to drive the pump 57.

However, as will be described hereinafter, when dumping of gas from the engine is initiated by an operator to reduce mean pressure in the working spaces of the engine 10, between, for example, mean pressures of l ,500 to 1,100 pounds per square inch absolute, using a preferred working embodiment of such an engine, the engine dumps through the dump header 53, regulator 48 and accumulators 56 and 56a directly into the reservoir 41. At this range of gas pressure, depending of course on the actual gas pressure in reservoir 41, gas entering into chambers 62 of the accumulators 56 and 56a would immediately flow back out through the valves 64 to the reservoir 41 and no work output from the compressor pump would be required. Below l,l00 pounds per square inch dump pressure, or otherwise as necessary, the compressor pump 57 is used to pump the gas back into the reservoir 41 in the manner described.

Referring now to FIG. 4, there is illustrated schematically in greater detail that portion of the gas flow system, outlined in broken lines in FIG. 2, relating to the interconnection of conduits between the fill header 46, engine 10 and dump header 53. As shown, the fill header 46 is connected by a conduit 51 to each of the cylinders 11 (the four cylinders in this figure being further identified as cylinders CYL-l, CYL-Z, CYL-3 and CYL-4), of the engine 10 through a cooler 31, regenerator 32 and heater tubes 33 for each of the cylinders, with each cylinder also being connected with the next cylinder, in the appropriate phasing order, by conduits 34 to provide four working spaces as previously described. Conduits 34 are also in communication with the conduits 52 interconnecting the cylinders to the dump header 53. Conduits 51 leading to out of phase cylinders CYL-l and CYL-3 are adapted to be placed in communication with each other by solenoid actuated bypass valve SV-2 in connecting conduit 86, while out of phase cylinders CYL-2 and CYLr-4 are adapted to be placed in communication with each other by solenoid actuated bypass valve SV-3 in connecting conduit 87.

In order to operate the engine at varying output torques and speeds ranging from idle to full ratedload, the pressure control regulator 48, as actuated by an operator, is used to vary the pressure of the working gas in the working spaces of the engine 10. The pressure control regulator 48 is connected by the conduit 47 to reservoir 41 in which a supply of working gas, preferably hydrogen, is kept under pressure.

Pressure control regulator 48 controls the supply of gas to the cylinders of the engine 10 through conduit 49 and fill header 46 connected to the engine, as previously described.

Pressure control regulator 48 is also connected to the engine working spaces through conduit 54 and dump header 53 to control the exhaust of gas from the working spaces through these conduits. Exhausted gas is transmitted to gas compressors 56 and 56a which increase the pressure of gas if necessary before it is returned to reservoir 41.

Pressure control regulator 48 may be made in any suitable form; however, a preferred arrangement for such a system is schematically shown in FIG. 5 of the drawings. As shown, the regulator 48 includes a fill valve 101 connecting through line 47 with reservoir 41 and through line 49 to the fill header 46 for the engine 10. Oppositely disposed from the fill valve is a dump valve 102. Dump valve 102 connects through conduit 54 with the dump header 53 to the engine working spaces and through line 55 with gas compressors 56 and 56a. I

A pivotally mounted actuating lever 103 is arranged between these valves 101 and 102 so as to open the fill valve 101 upon a downward movement and open the dump valve 102 upon an upward movement of the lever. Adjusting means such as screws 104 are provided to properly adjust the valve positions. The adjustments are preferably such that all valves are closed with the lever in an intermediate position and the dump valve 102 opens upon a slight upward movement and the fill valve opens upon a slight downward movement of the lever from the position shown.

This system further includes a cylinder 105 carrying a reciprocable piston 106, one end of which engages the underside of lever 103. The lower face of piston 106 is acted upon by gas pressure supplied through a capillary line 49a connecting the cylinder 105 with the engine working spaces. The capillary line acts to restrict gas flow so that cyclic pressure variations in the engine working spaces are not transmitted to cylinder 105, but changes in the mean workingpressure due to operation of the gas pressure control system are followed by the pressure in the cylinder 105.

The upper surface of lever 103 is engaged by a spring 107 which is partially compressed by a follower 108 controlled by a rotatably mounted cam 110. Cam 110 is in turn actuated by a gear 1 l 1 engaged by a rack 112 which is mechanically connected through linkage 113 with a manually actuated foot pedal 114. Adjustable stop means 115 are provided to be engaged by an abutment 116 on the rack to limit travel of the maniial-"a'ctuating means.

Beneath lever 103, an overspeed governor mechanism is provided comprising rotating flyweights 117 which engage a reciprocable shaft 118 urging the shaft upwardly against a spring 120 to engage the lower surface of lever 103. Flyweights 117 are rotated at a speed proportional to engine speed through mechanism, not shown.

When the engine is in operation, an increase in engine torque is obtained by moving pedal l 14 in a counterclockwise direction. This moves rack 112 leftwardly rotating cam 110 so as to increase the downward force of follower 108 on spring 107. Assuming the .mean working pressure acting on piston 106 is less than that called for, lever 103 is pivoted downward by the bias of the spring, opening valve 101 and permitting pressurized gas to flow from the reservoir 41 to the engine fill header 46 and then to the working spaces of the cylinders 11 of engine to increase the working pressure therein. The increase in mean working pressure is transmitted through line 49a to cylinder 105 acting against piston 106 and urging lever 103 upwardly until, when the desired pressure is reached, lever 103 resumes a neutral position closing valve 101 and shutting off the flow of gas.

If a decrease in engine torque is desired, pedal 114 is moved clockwise and through cam 110 reducing the downward bias of spring 107 and permitting piston 106 to move lever 103 upwardly opening dump valve 102. This permits the exhaust of gas from the working space through dump header 53 and lines 54 and 55 to the gas In case of an engine overspeed, flyweights 117 urge shaft 118 into engagement with lever 103 moving it upwardly and acting to exhaust working gas from the engine through the opening of dump valve 102.

The regulator 48 also includes a switch SW-2 actuated by lever 1.03 and a pressure actuated switch SW-3 in the electrical circuit for solenoid actuated bypass valves SV-2 and SV-3 used to effect rapid reduction of output torque from engine 10, as shown in FIG. 4. Switch SW-2 is a normally open switch which is closed, depending upon position of adjusting screw 104, when lever 103 moves upward for opening dump valve 102.v Switch SW-3, a normally closed switch, is opened by a pressure actuator 121 connected to conduit 49a whenever the pressure in this conduit is above a predetermined pressure, for example, above a pressure of 1,100 psia in the embodiment of the system disclosed.

Although the engine control system of the invention can be designed for any size engine or gas pressure conditions, a brief description of the system as applied to the engine disclosed operable under predetermined pressure conditions is as follows:

Fill of gas to the hot gas engine is always from the reservoir 41 through the engine pressure control regulator 4'8 and aforesaid conduits to the engine 10 by normal pressure flow. When the engine is empty, the reservoir contains a gas, such as hydrogen, at a pressure of 2,000 psia. Sufficient hydrogen is in the reservoir 41 to allow filling the entire engine system with gas at 1,500 psia mean working pressure. If leakage should occur during engine operation, the pressure in the reservoir 41 could drop below 1,200 psia at maximum engine pressure conditions. However, the supply tank 40, which serves as a secondary reservoir, is provided for makeup and contains sufficient gas therein to maintain a minimum gas pressure in the reservoir of 1,200 psia. The supply tank 40 also acts as a secondary reservoir for gas to bleed from the reservoir 41 if the pressure of the gas therein exceeds 2,000 psia at shutdown of the engine.

During normal engine operation, the operator actuates the foot pedal 1 14 to control the engine mean gas pressure through the pressure control regulator 48 as previously described. As more power is required, the pedal 114 is depressed further to further open the fill valve 101 resulting in higher mean working pressures in the engine. When the pedal 114 is lifted, a dump is initiated, in the manner previously described, to reduce the mean pressure of the gas in the engine through the discharge of gas therefrom.

As previously described, in the embodiment of the system disclosed, between mean pressures of 1,500 psia and 1,100 psia, the engine dumps gas directly into the reservoir 41, with the filling or dumping time being limited only by the line sizes of the interconnecting conduits between the various components of the system. Below a pressure of 1,100 psia for the dump gas, the compressor pump 57 is required to pump the gas back into the reservoir, the compressor pump 57 being sized so as to effect rapid pumping of the gas back into the reservoir 41, when necessary, up to a pressure of 2,000 psia.

While one of the accumulators 56 or 560 is connected to the discharge side of the compressor pump to effect compression of the gas contained in the com pressor accumulator, the oil chamber of the other accumulator is connected to the inlet of the compressor pump to create a suction within the accumulator chamber to further induce gas flow to the gas chamber of the accumulator from the dump header 53. The charge of gas thus drawn into this accumulator will then be compressed and forced back into the reservoir 41. The accumulator chambers are then reversed and the process continues until the operator calls for a fill of gas to the engine or the engine idle conditions have been reached. As previously described, an idle speed governor with flyweights 117 therein is built into the engine pressure regulator to effect dumping at excessive engine speeds.

By making the reservoir 41 about equal in volume to the volume of the working spaces in the engine 10 and its associated piping, optimum operating results can be obtained. With the reservoir thus sized, it has been found that the reservoir need not be too large, as compared to previously known systems, and that the pres sure of the gas in the system can be set so that the engine can be filled to the maximum gas pressure condition, so that, under normal conditions, the pressure of the gas remaining in the reservoir is about 200 psi above the minimum cycle gas pressure at full engine load conditions.

However, at full engine load conditions, the maximum working pressure of the gas is considerably higher than the pressure of the gas remaining in the reservoir 41 and allows the gases dumped from the 7 working spaces of the engine to be, in effect, pumped by the engine directly to the reservoir 41 with no extra compression of the gas by work output by the compressor pump 57. This direct dumping of gas from the engine working spaces can be done until the engine maximum cycle pressure gets to within approximately 200 psi of the pressure of the gas remaining in the reservoir 41. Below this pressure differential, the gas must be pumped into the reservoir 41 by operation of the compressor pump 57, but about one-third of the gas in the engine working spaces can be dumped back to the reservoir in this manner.

When compression is required, it is desirable to reduce the power required for operation of the compressor pump 57 to a minimum. This is accomplished by using a small low pressure reservoir 41 and by reducing the pressure differential against which the compressor pump 57 must operate. In the arrangement shown in FIG. 3, the inlet or suction to the compressor pump 57 is from an accumulator which is being charged with dumped gas from the engine, which gas is already under some pressure. Thus, the oil pump must perform work only to compress the dumped gas to overcome a pressure differential which is that existing between the engine maximum pressure and the pressure in the reservoir 41.

From the above description of the subject control system, it is apparent that there is provided a control system arrangement requiring the least engine power to operate. This advantage is obtained by means of the following:

The use of a reservoir of about equal volume with that of the engine to take full advantage of the engines pumping ability.

The use of a separate supply tank which allows the system to be maintained at optimum pressure conditions for extended periods of operation and independent of leakage or system temperature changes.

The i use of a pressurized compressor pump inlet which reduces the head requirement to a minimum.

The use of a non-vented piston which reduces the engine gas inventory and therefore the compressor pumping capacity requirement.

The use of the bypass torque control to reduce engine output torque while the compressor system is dumping gas and extend the time available for pumping thus reducing the horsepower requirement of the pump.

What is claimed is:

1. A power control system for a hot gas engine of the type having a plurality of closed variable volume working chambers each having a hot space and a cold space and adapted to contain a working gas, said engine including means for heating and for cooling such working gas and means to transfer such gas between said hot and cold chambers while passing it through a working cycle, said control system comprising: a gas storage reservoir means including a gas reservoir and a supply tank interconnected by a pair of conduits, one of which contains a pressure regulator valve to control the flow of gas from said supply tank to said reservoir and the other containing a one-way check valve connecting said reservoir to said supply tank, first gas transfer means connecting said reservoir with said engine working chambers for unidirectional gas flow from said reservoir to the individual chambers, second gas transfer means connecting said reservoir with said engine working chambers for unidirectional gas flow from the individual chambers to said reservoir, regulating means arranged to control the admission to and exhaust from said working chambers of working gas through said first and second gas transfer means respectively and a gas pump in said second gas transfer means between said regulating means and said reservoir an ada ted to aid the r turn 0w of as to said reservoi r wh en the return flow o f gas lS below a predetermined pressure relative to the pressure of gas in the reservoir while permitting direct return flow of gas to said reservoir when the return flow of gas is above a predetermined pressure relative to the pressure of gas in the reservoir.

2. A power control system according to claim 1 wherein said gas reservoir is sized in respect to the volumes of said engine working spaces and the components of said first and second gas transfer means such that said volumes can be supplied with gas from said reservoir to the maximum mean working pressure condition from only said reservoir, additional gas from said supply tank flowing to said reservoir at a predetermined pressure below the maximum mean working pressure through said pressure regulator valve.

3. A power control system according to claim 1, further including bypass valve means interconnecting out of phase pairs of said closed variable volume working chambers to permit the bypassing of gas from said out of phase working chambers to effect rapid reduction of engine output torque thereby and pressure responsive means and manually actuated lever means in said regulating means to effect operation of said bypass valve means. 

1. A power control system for a hot gas engine of the type having a plurality of closed variable volume working chambers each having a hot space and a cold space and adapted to contain a working gas, said engine including means for heating and for cooling such working gas and means to transfer such gas between said hot and cold chambers while passing it through a working cycle, said control system comprising: a gas storage reservoir means including a gas reservoir and a supply tank interconnected by a pair of conduits, one of which contains a pressure regulator valve to control the flow of gas from said supply tank to said reservoir and the other containing a one-way check valve connecting said reservoir to said supply tank, first gas transfer means connecting said reservoir with said engine working chambers for unidirectional gas flow from said reservoir to the individual chambers, second gas transfer means connecting said reservoir with said engine working chambers for unidirectional gas flow from the individual chambers to said reservoir, regulating means arranged to control the admission to and exhaust from said working chambers of working gas through said first and second gas transfer means respectively and a gas pump in said second gas transfer means between said regulating means and said reservoir and adapted to aid the return flow of gas to said reservoir when the return flow of gas is below a predetermined pressure relative to the pressure of gas in the reservoir while permitting direct return flow of gas to said reservoir when the return flow of gas is above a predetermined pressure relative to the pressure of gas in the reservoir.
 2. A power control system according to claim 1 wherein said gas reservoir is sized in respect to the volumes of said engine working spaces and the components of said first and second gas transfer means such that said volumes can be supplied with gas from said reservoir to the maximum mean working pressure condition from only said reservoir, additional gas from said supply tank flowing to said reservoir at a predetermined pressure below the maximum mean working pressure through said pressure regulator valve.
 3. A power control system according to claim 1, further including bypass valve means interconnecting out of phase pairs of said closed variable volume working chambers to permit the bypassing of gas from said out of phase working chambers to effect rapid reduction of engine output torque thereby and pressure responsive means and manually actuated lever means in said regulating means to effect operation of said bypass valve means. 